At the present time, there is no satisfactory mechanism by which male contraception can be achieved with a high degree of reliability while being practiced and yet be completely reversible. This proposal is designed to examine this problem. The experimental animal of choice is the mature male squirrel monkey. The reproductive system of this primate undergoes cyclic variation from quiescent to sexually active stages. This condition "naturally" fulfills the criteria of effective, yet reversible contraception. The techniques used in this investigation include light and electron microscopy, histochemistry and radioautography. The correlation between morphology and function of the testis, epididymis and seminal vesicles of the sexually active and quiescent mature squirrel monkey will be studied. It is hoped that this will establish the "base line" for the evaluation of experimental work.